IB Biology HL Option A.2

Describe how heart rate is controlled by the medulla.

- cardiovascular centre of medulla regulates rate of heartbeat - blood pH and pressure monitored by receptors in blood vessels and medulla which cause cardiovascular centre to increase/decrease heart rate by sending signals to pacemaker - signals carried from sympathetic system speeds up heart rate - signals carried from parasympathetic system decreases heart rate

What has caused the enlargement of the cerebral cortex of humans?

- cerebral cortex has become enlarged during human evolution and contains more neurons than any other animal - increase due to increase in total area with extensive folding to accommodate brain inside enlarged cranium which forms shape of skull

What is the role of the primary motor cortex? How does it work? Where is it located?

- controls muscles throughout the body - primary motor cortex in left cerebral hemisphere controls muscle contractions in right side of body and vice versa - located in posterior part of frontal lobe

How can the pupil reflex can be used to evaluate brain damage?

- doctors use pupil reflex to test brain function by shinning light into eye - if pupils do not constrict then medulla oblongata is probably damaged and patient is pronounced brain dead

Explain how sensory inputs are transferred to the left and right cerebral hemispheres.

- left cerebral hemisphere receives sensory input (e.g. tactile sensation) from sensory receptors on right side of body, transferred via spinal cord - left cerebral hemisphere processes visual information from right visual field of both eyes, transferred at optic chiasma - and vice versa for right hemisphere

Describe how size of pupil is controlled and effect of signals from sympathetic and parasympathetic systems.

- muscles in iris control size of pupil - impulses carried by neurons of sympathetic system cause radial muscle fibres to contract which dilates pupils - impulses carried by neurons of parasympathetic system cause circular muscle fibres to contract which constricts pupils

What animals have a cerebral cortex? How do theirs compare to the human cerebral cortex?

- only mammals have cerebral cortex with varying sizes - forms larger proportion of brain in humans than any other mammal - also more highly developed in humans

What is the role of the pituitary gland?

- posterior lobe stores and releases hormones produced by hypothalamus - anterior lobe produces and secretes hormones that regulate many body functions

Describe how fMRI can be used to identify roles of different parts of brain.

- records changes in blood flow within brain to identify activated areas via injection of harmless dye - low resolution scans taken when subject is given stimulus

Describe how animal experiments can be used to identify roles of different parts of brain. Include concerns and limitations.

- used to identify function by stimulating regions with electrodes or removing skill via lobotomy to complete experimental procedures - highly invasive and potentially damaging therefore, animal models often used - limited by differences between animal and human brains

Define lesions. How are they identified?

abnormal areas of brain tissue which can indicate effect of loss of brain area - identified via autopsy or CT/MRI scans

What is the role of the cerebral hemispheres?

acts as integrating centre for highly complex functions e.g. learning, memory, emotions - functions involve stimuli from different sources e.g. eye, ear, memories and rely on complex network of neurons

State 4 methods which can be used to identify roles of different parts of brain.

animal experiments, lesions, autopsy, fMRI

What part of the brain does the cerebral cortex form?

cerebral cortex forms a larger portion of the brain

What is the role of the autonomic nervous system? Identify the two different components. What are the effects of the two parts?

controls involuntary processes using centres in medulla oblongata (and brain stem) - two parts: sympathetic and parasympathetic - opposite effect on involuntary processes

What is the role of the cerebellum?

coordinates unconscious functions e.g. posture, non-voluntary movement and balance

Explain how the brain, spinal cord and PNS form from the neural tube.

during embryonic development neural tube enlarges and develops into different parts of nervous system: - most becomes spinal cord - anterior end expands and develops into brain during cephalization (development of head) - cells from neural crest differentiate to form most of PNS

Where does the energy used by the human brain come from?

energy comes from aerobic cell respiration which requires lots of glucose

What does the human brain use energy for?

energy used by brain to sustain neurons and processes: - energy needed to maintain resting potential and re-establish it after action potential - energy used for synthesis of neurotransmitters and other signal molecules

What does fMRI stand for?

functional magnetic resonance imaging

How much energy does the human brain require?

human brain uses over 20% of body's energy

What is the role of the hypothalamus?

interface between brain and pituitary gland (maintains homeostasis) - synthesises hormones secreted by posterior pituitary - releases factors that regulate secretion of hormones by anterior pituitary

NOS: What is sensory homunculus?

models of body in which size of each part corresponds to proportion of somatosensory cortex devoted to sensory inputs from that part

Describe the function of the nucleus accumbens. Where is it located?

pleasure/rewards centre of brain - stimuli (e.g. food, sex) causes release of neurotransmitter dopamine in nucleus accumbens which causes feelings of well-being, pleasure and satisfaction - located in each cerebral hemispheres

What is the correlation between brain size and body size in different animals?

positive correlation but relationship is not directly proportional

Define autopsy.

post-mortem exam of corpse via dissection to evaluate causes of death

Describe how swallowing is coordinated by the medulla.

process of swallowing where food passes from pharynx to stomach via oesophagus is involuntary and is controlled by swallowing centre of medulla oblongata

Explain the pupil reflex.

pupil reflex occurs when bright light suddenly signs into eye: - photoreceptive ganglion cells in retina perceive bright light and send signals through optic nerve to mid-brain which activates parasympathetic system - pupil constricts to reduce light entering eye which protects retina from damage

Describe the function of the visual cortex. Where is it located?

region of brain responsible for sight - receives neural impulses from light-sensitive cells in retina - located in occipital lobe of cerebrum

Describe the function of Broca's area. Where is it located?

responsible for speech production - if damaged person cannot speak properly despite intending to - located in frontal lobe of left cerebral hemisphere

NOS: What does the motor homunculus show?

shows proportion of motor cortex that is devoted to control of muscles in each part of body

What are the 2 nervous systems of the PNS?

somatic (voluntary) and autonomic nervous systems

Describe how breathing is controlled by the medulla.

two centres in medulla control breathing: 1. controls timing of inspiration 2. controls force of inspiration and active voluntary expiration chemoreceptors in medulla monitor blood pH: - decrease in blood pH indicates increase is carbon dioxide making breathing deeper and more frequent

What is the role of the medulla oblongata?

used in automatic control of gut muscles, breathing, blood vessels and heart muscle